No Ordinary Man: A Life of George Carman Dominic Carman 309pp, Hodder, £18.99

It is a well-known plank of British law that you cannot libel the dead. Dominic Carman was undoubtedly wise to wait until his father was safely interred in the Catholic cemetery at St Mary's, Kensal Rise, before publishing this biography of the legendary defamation silk.

According to Dominic Carman, it was his dying father's idea that his only son should write his life story. If so, then he must have assumed that the biography would be informed by some strand of filial affection and loyalty. Never in his worst nightmares could he have anticipated that his son would have produced this searing account of his life, lucratively serialised - and embellished with additional material - in the Sunday newspapers. That is not to say that No Ordinary Man is a bad book, or even a dishonourable book. But you cannot read it without wondering at the motivation of the author. Few sons would set out to lay bare a father's human flaws in such excruciatingly raw detail.

Those who worked closely with Carman knew of some of his weaknesses. He was a private man who seemed to lead an empty and lonely life away from the law. He was bad at holding his drink. He could be difficult and ill-tempered. His insecurity and vanity were always near the surface. But those whose contact with him did not extend beyond the triple boundaries of chambers, courtroom and wine bar could not have guessed at the extent of the difficulties and personal flaws that - at least according to his son - lay behind his complex mask.

It is evidently Dominic Carman's strong wish that we should know more. He wants the world at large to know that his father was habitually so drunk he had to be helped into bed; that he was in all probability bisexual; that he may have been sexually abused as a boy; that he blew millions at the gambling tables; that he suffered from prolonged periods of impotence; that he was repeatedly violent towards all three of his wives; that he was a poor father and uninterested grandfather; that he spent much of his life one step ahead of the bailiffs.

All this, and much more, is packed into Dominic Carman's portrait. His preface suggests that while writing it was difficult, he felt he had no alternative: "To those who will argue that many things would have been better unsaid, I can only comment that after a lifetime of enforced silence, there is no choice other than to tell the truth."

This is a bit disingenuous of young Dominic. His father's former client, Jeremy Thorpe, could have told him that there are times when keeping silent is not a bad tactic. And George himself could have given his son entire seminars on the difference between the truth, the whole truth and nothing but the truth. A self-conscious assertion that you have told the truth invites sceptical inquiry. It appears, for instance, that Dominic Carman's eldest son, Matthew, does not recognise his grandfather from this book. He wrote a letter to the Guardian last week contradicting his father's account of their relationship, adding pointedly: "It saddens me deeply that the greatest defender of our time is not here to defend himself."

The newspaper serialisation added further, better and more intrusive particulars about Karen Phillipps, the woman who shared the last 15 years of Carman's life. It is plain that Dominic Carman intensely dislikes Ms Phillipps, though whether the cause is Freudian, financial or the straightforward rivalry of two biographers chasing the same subject is not clear. The dislike is evidently reciprocated. Whatever their motivation, some of the allegations about Ms Phillipps have also been contradicted. The simple sword of truth can be an unwieldy and not very accurate weapon.

Two chapters in particular may help the reader decide why Dominic Carman has painted such an unflinching portrait of his father. The first chapter is a potted autobiography - Dominic's childhood, his marriages, his divorce, his failings as a father and husband and professionally; his own insecurities. While he doesn't explicitly blame these disappointments on his unconventional and difficult upbringing, it does read like an attempt at, as it were, posthumous rationalisation - a belated bash at explaining to his late father why he could never measure up to his hopes or expectations.

The other revelatory chapter is the penultimate one, in which all three of Carman's former wives are given space to reveal, in their own words, the stories of their failed marriages. Each relationship, according to these narratives, began well, but soon deteriorated into a sort of hell of debt, abuse, drink, absence, sexual inadequacy and violence. Carman is, as his grandson says, unable to defend himself. But there is enough of a consistent pattern in these statements - partly corroborated by Dominic Carman himself - to suggest that they are fair accounts of what it was like to be married to Carman.

Uncomfortable though these testimonies are, it is difficult to deny the right - some would even argue duty - of these women, Ursula, Celia and Frances, to tell their stories. If Carman was indeed abused as a child, then this is a familiar cycle of the abused becoming the abuser. Which is, as they say, a plea in mitigation rather than a defence.

Many who liked Carman and others who have cause to be grateful to him will find these sections distressing. They will struggle to reconcile the mischievous, gossipy friend and the loyal, tenacious advocate of fond memory with this new and disturbing evidence of a bullying, and at times frightening, domestic tyrant. But then that struggle to reconcile the good and the bad, the admirable and the ugly, is at the heart of Dominic Carman's own exploration.

So much for what had hitherto been the private side of George Carman's life. What of the more familiar public career as legal showman - the greatest jury advocate of his generation, the eviscerator of anyone unfortunate enough to step into a witness box without having taken the advance precaution of retaining him?

Here the book is more patchy. Dominic Carman canters through the highlights of his father's best-known cases without, in most instances, adding much to the existing public record. The stories are well told, with plenty of quotations from the classic set-piece cross-examinations and carefully prepared final speeches. But, in most cases, there are few fresh disclosures or inside angles.

The main exception is the Aitken case, which required Carman - already quite ill with cancer - to perform the longest and most difficult cross-examination of his career. Dominic Carman has interviewed Aitken, as well as his silk, Charles Gray QC, and the judge, Sir Oliver Popplewell. Aitken's view apparently remains that his bravura performance in the witness box had sufficiently convinced the judge that without the dramatic and damning last-minute evidence from British Airways, he would have been home and dry.

"My hunch was that I would have won the case outright... I think [Popplewell] may well have harboured serious doubts about the [dispute over who paid the bill at the] Ritz, but... from his questions, his attitude, his body language, I think he was on our side and was likely to accept that I should be the winner in this case."

Such was Aitken's view, which was shared by his counsel - not to mention several others watching Sir Oliver's every tic and grimace (he was sitting without a jury, so the verdict and damages depended on him and him alone). They are, apparently, all wrong. Sir Oliver told Dominic Carman that he wasn't fooled for a moment: "I just didn't believe a word he said on the Ritz. George hadn't gone very far before he'd achieved his objective as far as I was concerned: he'd persuaded me that Aitken's account of the Ritz was untrue. It was absolutely fixed in my mind that the story was false... I had made up my mind that I would not find for Aitken."

Sir Oliver's verdict is a slap in the face for the small but devoted band of Aitken loyalists who persist in believing that the former defence minister would have romped home had he not been tripped up at the last fence by the production of the air tickets - a knock-out blow described by Carman as "the most dramatic moment in my professional life".

Dominic Carman has written a strange, unsettling book. It is, by turns, funny, painful, voyeuristic, Pooterish, muddled, touching, unbalanced, amateurish, painful, racy, angry and - despite it all - affectionate. His father would have hated it. There is no doubt that, were he still alive, he would have moved legal heaven and earth to prevent the book's publication. But the dead can't sue - a technicality which has robbed us of what might have been the ultimate case: Carman v Carman.